Method for increasing the viscosity of liquid polymeric dimethyl silicone



Patented Apr. 19, 1949 METHOD FOR INCREASING THE VISCOSITY OF LIQUIDPOLYMERIC DIMETHYL SILI- CONE J ames Franklin. Hyde, Corning, N. Y.,asslgnor to Corning poration of New York No Drawing, 1 Application March30, 1943, Serial No. 481,155

1 Claim. 1

This invention relates to new compositions of matter, their preparationand uses and, more particularly, to organo-siloxanes and methods ofpreparing them.

This application is a continuation-in-part of my copending applicationsSerial No. 318,373, filed February 10, 1940, Serial No. 353,302, filedAugust 19, 1940, and Serial No. 432,529, filedFebruary 26, 1942, allassigned the assignee of the present invention. These applications arenow Patents Nos. 2,386,466; 2,371,050 and 2,438,478, re-

- spectively,

siloxanes which are within the scope of my invenv tion. In the lattercase, a hydrolyzable silicane which contains no organic radicalsattached to silicon through a carbon atom, such as silicontetrachlorideor ethyl orthosilicate, may be ineluded alongwith the hydrolyzableorgano-silicanes. By hydrolyzable organo-silicanes I mean derivatives ofSiH4 which contain readily hydrolyzable radicals such as hydrogen,halogens, amino groups, alkoxy, aroxy and acyloxy radicals, etc., theremaining valences of the silicon atoms being satisfied by organicradicals that are joined to the silicon atoms through carbon atoms suchas alkyl, substituted alkyl, aryl, substituted aryl radicals, etc.

Hydrolysis of the above silic'anes or mixtures thereof is generallyconcurrently accompanied by condensation to a greater or less degreedepending upon the conditions of hydrolysis and the particular silicanesinvolved. As a result of the hydrolysis and concurrent condensation,organesilicon oxide polymers or organo-siloxanes are produced which arepartially or completely condensed and which have on the average up toand including three organic radicals attached to each silicon atom. Thepolymers so obtained vary in Icharacter, some being oily liquids, othersbeing crystalline solids or gels. They also vary in the ease with whichthey may be further polymerized by heat since they differ in the numberof active Glass Works, Corning, N. Y., a corfunctional groups retainedas a result of incomplete hydrolysis and condensation. Those which areonly partially condensed may be converted to higher polymers and even tosolids by heat alone or even by standing at room temperature by virtueof the completion of condensation. On the other hand, thoseorgano-siloxanes which approach complete condensation are extremelyresistant to further polymerization by heat alone. These substantiallycompletely condensed polymers are not limited to those which are of highmolecular weight but may be polymers of low molecularweight as well. Forexample, the condensed hydrolysis products of the di-organosilicanes areessentially completely condensed even in the low polymeric stages andexist generally in the trimeric form with polymers as high as thehexamer being reported in only rare instances. Since the higher polymersof these organo-silicon oxide compounds, and particularly the higherpolymers of the substantially completely condensed compounds, have beenfound to possess properties which adapt them to many industrialapplications as will be described below, it is highly desirable toprovide a method of further polymerizing the organo-silicon oxidepolymers to higher polymeric compositions, that is, to increase theiraverage molecular weight.

The primary object of this invention is to provide a method ofpolymerizing the hydrolysis products of hydrolyzable organo-silicanes ormixtures thereof.

Another object of my invention is to provide a method of furtherpolymerizing an organo-silicon oxide polymer having on the average lessthan three organic radicals attached through carbon atoms to eachsilicon atom.

Another object of my invention is to provide a method of furtherpolymerizing a substantially completely condensed liquid hydrolysisproduct of a silicane of the type RaSiXz, where each R is an organicradical which is joined to the silicon atom through a carbon atom andeach X is a hydrolyzable atom or group.

Still another obiectof the present invention is to provide a method ofpolymerizing a substantially completely condensed liquid hydrolysisproduct of a mixture comprising essentially a di-organo-substitutedsilicane to a polymeric composition which is substantially free of poly*mers having less than seven silicon atoms per molecule.

Another object of my invention is to provide a methodof polymerizing toa heat convertible state a liquid organo-silicon oxide polymer having onpare organo-silicon oxide polymers of high av-,

erage molecular weight which are infusible resinous solids.

In accordance with my invention, I have provided a method of preparingan extremely useful polymeric composition from" the hydrolysis productof a hydrolyzable organo-silicane or of a mixture of hydrolyzablesilicanes which comprises maintaining an acid catalyst in intimate andcontinuous contact with the hydrolysis product under polymerizingconditions until a polygenerally applicable to those polymers having318,373 filed February 10, 1940, of which the present application is acontinuation-impart, I

showed that the hydrolysis products of aryl silicanes could bepolymerized to high polymers by treatment with aqueous hydrochloric acidat elevated temperatures. It was pointed out in that application thatsuch polymerization was meric composition having the properties desiredis obtained. If desired, the acid catalyst may be added during theinitial hydrolysis and condensation of the silicane or mixture ofsilicanes. However, it is important, especially in the case of theliquid hydrolysis products which are substantially completely condensed,that the acid catalyst be maintained in intimate and continuous contactwith the treated polymer until the desired higher polymer is obtained;for I have found that an appreciable increase in average molecularweight does not'occur until the poymer has been so treated for sometime. After this induction period, the viscosity and average molecularweight of the treated material rises rapidly until a stage ofpolymerization is reached where the acid catalyst is no longer necessaryto continue the polymerization but heat alone in the presence of air issufficient to convert the polymer to an infusible resinous solid. Thoseorgano-siloxanes which are initially only partially condensed, ofcourse, do polymerize by heat alone but I have found that treatment inaccordance with my invention not only increases the rate ofpolymerization but produces flexible resinous solids instead of themechanically weak gels ordinarily obtained by heat alone. In carryingout my method, I prefer to use as acid catalysts acids of the so-calledstrong type i. e. the hydrohalic acids, sulphuric acid, phosphoric acid,oxalic acid, etc. I have also found that the addition of water in theform of steam during the polymerization process aids in speeding up thepolymerization. The particular concentration and quantity of acidemployed and the optimum temperature for carrying out the-polymerizationare conditions which vary with the organo-siloxane being treated andalso with the type of polymer desired as will be readily apparent fromthe examples given below. However, I prefer to carry out thepolymerization at a temperature within the range from about 100 C. toabout 250 C.

In general, any liquid organo-silicon oxide polymer having on theaverage less than three organic radicals attached through a carbon atomto each silicon atom may be polymerized by my method; that is. treatmentin accordance with my method will result in an increase in averagemolecular weight. My method is not probably accomplished by the removalof the aryl groups and linking together of lower poly-' meric units toform higher polymers. I have since discovered that furtherpolymerization of the organo-siloxanes is not limited to the arylsiloxanes but applies equally well to all organosiloxanes. However,while polymerization in the case of aryl slloxanes may result upon thehydrolyzing of the aryl groups themselves, it is believed that a morefundamental phenomenon is involved which applies'to allorgano-siloxanes, namely, that the 81-041 bonds present in theseproducts will rupture and rearrange on continued exposure to acid atelevated temperatures so that higher polymeric compositions may beformed even from polymers which contain few, if any, functional groups.Failure on the part of early workers in the field to appreciat theeffect of acid upon the extremely stable Si-O-Si bond and the fact thatany acid produced in the hydrolysis of the organo-silicon halides wasspeedily driven off in the gaseous form upon the application of heatbefore its effect could be felt probably accounts for the failure todiscover that the hydrolysis products could be polymerized to materialsof high molecular weight by acids.

The high polymers produced in accordance with my invention have beenfound to be particularly well adapted to be employed as pro tectivecoatings, especially in the field of electrical insulation. Extremelyviscous fluids whose final viscosity can be controlled by the conditionsof acid treatment are readily prepared which,

when applied as impregnants to glass insulating tape or directly tometallic conductors and upon being heated, set to adherent and infusiblecoatings having varying degrees of toughness and flexibility dependingalso upon the particular conditions of acid treatment as well as uponthe substituents present in the polymer. These coatings are heatresistant, imprevious to moisture and electrically non-conducting.

For a better understanding of my invention reference should be had tothe following examples.

Ezrample 1 Thirty grams of phenyl ethyl silicon dichloride weredissolved in cc. of ethyl ether and then added dropwise to excess waterat room temperature. The resulting mixture was allowed to stand forseveral days. The ether and water layers were then separated. The etherlayer was dried at room temperature under a vacuum to constant weight.An oily liquid was produced which analysis showed to be the completelydehydrated cyclic trimer of phenyl ethyl silicone. The latter was heatedat about l70-l80 C. while at the same time aqueous hydrochloric acid wasadded dropwise. The liquid became increasingly viscous. Continuedheating at about l80 C. with continued addition of hydrochloric acidafter several hours brought the material to a sticky, viscous state, inwhich state it was soluble in toluene and other organic solvents. Thismaterial was found to have an average molecular weight of 1310. Thiscorresponds closely to a polymer having 12 silicon atoms per molecule.Further heating at a somewhat higher temperature converted it to aflexible non-tacky resinous substance which was infusible and insoluble.Substantially the same kind of product was obtained when phenyl ethylsilicone was treated in like manner with .2% by weight of sulphuric acidin the neighborhood of 200 C.

Example 2 A sample of trimeric phenyl ethyl silicone was heated to about180 C. A quantity of 85% phosphoric acid equal to about 1.5% by weightof the silicone was added with stirring to the silicone. The mixture waskept at 180-190 C. until the viscosity of a 50% solution of the productin toluene at 25 C. reached 50 centipoises. The phosphoric acid wasremoved by washing with excess calcium hydroxide, leaving a toluenesolution which served as an excellent coating composition for glassfibre tape.

Example 3 A mixture of dimethyldiethoxysilicane and 85% sulfuric acid inthe ratio of 2:1 by volume'was stirred for a few minutes. An oily liquidwas produced. This liquid was heated between 100 C. and 200 C. for aboutten hours. The resulting polymer was extremely viscous and soluble inbenzene. A solution of the polymer in benzene was applied to some glassfibre tape which was then baked for 20 hours at 130 C., for 48.hours at250 C., and for 100 hours at 300 C. After a few hours of the baking anadherent, non-tacky and flexible coating was produced which retained itsnon-tackiness and flexibility throughout the entire baking process.

Example 4 cc. of monobutyltriethoxysiliethyl alcohol and 1.4 cc. of 10 Nsulfuric acid was held at 30 C. for 21 hours. 3 cc. of carbitol acetatewere then added to the mixture in order to facilitate the removal ofalcohol and water in the subsequent desiccation. The entire mixture wastransferred to an aluminum dish in a desiccator where it was maintainedunder vacuum for 24 hours. The alcohol and water were thereby removed.The aluminum dish and its contents were then placed in an oven at 100 C.for 3 days. The temperature was raised to 150C. and held there for aday; at 170 C. for two days; and at 300 C. for a day. The product was aninsoluble and infusible horny resin.

A mixture of 10 cane, 10 cc. of 95% Example 5 A sample of phenyl methylsilicone (prepared by the hydrolysis of phenyl methyl silicon dichloridein the same manner as was the phenyl ethyl silicone in Example 1) washeated at about 100-150 C. At the same time aqueous hydrochloric acidwas added in small increments. Continued heating at about 170-180 C.with continued addition of aqueous hydrochloric acid brought thematerial to a sticky, viscous state after a few hours in which state itwas still soluble in toluene and was heat convertible. Further heating,at still higher temperatures, converted the silicone to a flexible,non-tacky resinous substance which was infusible and insoluble.

Example 6 A sample of tetrameric dimethyl silicone was refluxed withalcoholic hydrochloric acid for several hours. A high viscosity oilwasproduced having very little flow at room temperature.

Example 7 Liquid dimethyl silicone having a viscosity of 3.6 centistokeswas mixed with 10 N hydrochloric acid and refluxed. The following tableshows the viscosity at different times-of reflux.

Time of reflux: Viscositydn centlstokes 3 6 0 8 hours 6.0 15 hours 49.022 hours '75.!

The table clearly demonstrates the importance of Example 8 product was aresinous tacky material, soluble in viscosity in solution of C. Appliedfrom a toluene tape it dried (after removal toluene and having a 420centistokes at 25 solution to glass fibre of solvent) in 3 hours ofbaking at 250 C. to a heat resistant, tack-free resin.

Example 9 A mixture of ethyl silicon .trichloride, phenyl silicontrichloride, phenyl ethyl silicon dichloride, diphenyl silicondichloride, diethyl silicon dichloride and diphenyl ethyl siliconmonochloride (prepared by reaction of silicon tetrachloride, phenylmagnesium chloride and ethyl magnesium chloride in molar ratio of 1-1-1at 20 C.) was dissolved in ether and hydrolyzed with water. The ethersolution was washed free of acid and the ether removed by distillation.The resulting copolymer material was polymerized to a viscous, tackymaterial by heating at 220 C. with .2% by weight of H2804 while blowingwith steam. The material was soluble in toluene and when applied from atoluene solution to glass fibre tape it dried (after removal of solvent)within a few hours of baking at 250 C. to a heat resistant tack-free notincluding three radicals per silicon atom have been polymerized inaccordance with this invention. These copolymers were prepared by thecohydrolysis and co-condensation of mixtures ofdiiferently substitutedhydrolyzable silicanes obtained directly as mixtures from the Grignardreaction or prepared by mixing diiferent silicanes of fair degree ofpurity to give mixtures of desired constituents in predeterminedquantities. Among the silicanes employed to accomplish the latter wassilicon tectrachioride, ethylorthosilicate, methyltriethoxysilicane,dimethyldiethoxysilicane, trimethylethoxysilicane,phenylmethyldiethoxysilicane, phenyldimethylethoxysilicane,phenyltriethoxysilicane, d i p h e n yldiethoxysilicane,ethyltriethoxysilicane, diethyi silicon dichloride, pheny ethyl silicondichloride, butyltriethoxysilicane, dibutyldiethoxysilicane,benzyltriethoxysilicane, dibenzyldiethoxysilicane and others. Besidesthe catalysts designated in the examples, others were used includingnitric acid, gaseous hydrogen chloride, hydrobromic acid, boric acid,oxalic acid and benzene sulphonic acid.

My invention is applicable to any organosilicon oxide polymer having onthe average less than three organic radicals attached to each siliconatom through carbon atoms. Theunusual properties of these polymers aredue primarily to the SiOSi groups present therein and to the organicradicals attached to the silicon atoms. The kind and number of organicradicals attached to silicon do not affect the fundamental behavior ofthe polymers, but only modify certain particular properties thereof.Besides the organic radicals already disclosed such radicals may bepresent as propyl, isopropyl, amyl, hexyl, heptyl to octadecyl andhigher; alicyclic radicals such as cyclopentyl, cyclohexyl, eta; aryland alkaryl radicals such as monoand poly-alkyl phenyls as tolyl, xylyl,mesityl, mono-, di-, and tri-ethyl phenyls, mono-, di-, and tripropylphenyls, etc.; naphthyl, monoand polyalkyl naphthyls as methyl naphthyl,diethyl naphthyls, tri-propyl naphthyl, etc.; tetrahydronaphthyl,anthracyl, etc.; aralkyl such as benzyl, phenylethyl, etc.; alkenyl suchas methallyl, allyl, etc.

The new polymers may be used for. various purposes. For example, asalready mentioned, they are excellent coating and impregnating agents,particularly in the fabrication of electrical insulating materials,because in their intermediate form they can be dissolved and applied inthe form of solutions for the impregnation of various fibrous materialsand thereafter can be polymerized to complete insolubility andinfusibility. In the latter state they have good mechanicalcharacteristics and good electrical properties at room temperature, allof which are retained at temperatures above those at which prior coating,materials break down and deteriorate. The new polymers are relativelynonflammable and are likewise superior to prior coatings in that underextreme conditions of temperature, etc. there is little tendency tocarbonize.

In making use of the new polymers for impregnating tapes and otherfibrous materials for electrical insulation the polymerization iscarried out until the material has attained the sticky, viscousheat-convertible state just short of insolubility. Then, if desired, theacid may be removed by neutralization with alkali such as sodiumhydroxide or calcium hydroxide. The alkali, when added in excess, alsoserves to remove impurities that may be present such as iron, etc. Theneutralized product is dissolved in toluene or other suitable solvent.The solution is applied by dipping, brushing or spraying,

' until the viscous polymeric mixture is converted to a tack-freecoating. With the phenyl ethyl silicone polymer, this condition isattained by baking for about 36 hours while the temperature is slowlyraised from about 200 C. to about 260 C. Other organo-silicon polymerswithin the scope of my invention may require diflerent temperatures andtimes, but such conditions are readily determined by trial.

In addition to the use of the new polymers in the field of electricalinsulation, there are many others for which these polymers at variousstages of polymerization are eminently adapted. They may be used ashydraulic fluids, liquid insulating media, thermal expansion fluids,waterproofing agents, etc. Their resistance to high temperature, theirelectrical insulating properties, low freezing points and low vaporpressure adapt them to many diversified industrial applications.

I claim:

The method of increasing the average molecular weight of a completelydehydrated liquid polymeric dimethyl silicone which comprises addinghydrochloric acid to said silicone and refluxing the resulting mixtureof said silicone and hydrochloric acid until an increase in viscosity ofsaid silicone is effected.

JAMES FRANKLIN HYDE.

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